thunder

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The acoustic radiation produced by thermal lightning channel processes. The lightning return stroke is a high surge of electric current that has a very short duration, depositing approximately 95% of its electrical energy during the first 20 microseconds. Spectroscopic studies have shown that the lightning channel is heated to temperatures in the 20,000–30,000 K (36,000–54,000°F) range by this process. The pressure of the hot channel exceeds 10 atm (>10⁶ pascals). The hot, high-pressure channel expands supersonically and forms a shock wave as it pushes against the surrounding air. Because of the momentum gained in expanding, the shock wave overshoots, causing the pressure in the core of the channel to go below atmospheric pressure temporarily. The outward-propagating wave separates from the core of the channel, forming an N-shaped wave that eventually decays into an acoustic wavelet. See also Shock wave; Storm electricity.

The sound that is eventually heard or detected, thunder, is the sum of many individual acoustic pulses, each a remnant of a shock wave, that have propagated to the point of observation from the generating channel segments. The first sounds arrive from the nearest part of the lightning channel and the last sounds from the most distant parts.

The higher the source of the sound, the farther it can be heard. Frequently, the thunder that is heard originates in the cloud and not in the visible channel. On some occasions, the observer may hear no thunder at all; this is more frequent at night when lightning can be seen over long distances and thunder can be heard only over a limited range (∼10 km or 6 mi). See also Lightning; Thunderstorm.

noun

An earsplitting, explosive noise: bang, blast, boom, roar. See sounds/pleasant sounds/unpleasant sounds/neutral sounds or silence.

verb

To make an earsplitting explosive noise: bang, blast, boom, roar. See sounds/pleasant sounds/unpleasant sounds/neutral sounds or silence.

When a stroke of lightning passes through the atmosphere, the air becomes intensely hot, perhaps to 30 000 °C. The violent expansion thus caused makes a shock-wave heard as thunder.

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Thunder may indicate a loud knocking at the door of the dreamer's conscious mind to force the dreamer to pay attention and to learn. If accompanied by lightning bolts, inspiration and enlightenment may be indicated.

The noise created when air rushes back into a region from which it has been expelled by the passage of lightning.

• Maximizers and Superlatives

For other uses, see Thunder (disambiguation).

Thunder is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, thunder can range from a sharp, loud crack to a long, low rumble (brontide). The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within a bolt of lightning. In turn, this expansion of air creates a sonic shock wave which produces the sound of thunder, often referred to as a clap, crack, or peal of thunder. The distance of the lightning can be calculated by the listener based on the time interval from when the lightning is seen to when the sound is heard.

	Thunder A short sample of a crack of thunder
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Contents 1 Cause 2 Etymology 3 Calculating distance 4 See also 5 References 6 External links

Cause

Cumulonimbus clouds often form thunderstorms.

The cause of thunder has been the subject of centuries of speculation and scientific inquiry. The first recorded theory is attributed to the Greek philosopher Aristotle in the third century BC, and an early speculation was that it was caused by the collision of clouds. Subsequently, numerous other theories have been proposed. By the mid-19th century, the accepted theory was that lightning produced a vacuum. In the 20th century a consensus evolved that thunder must begin with a shock wave in the air due to the sudden thermal expansion of the plasma in the lightning channel.^[1] The temperature inside the lightning channel, measured by spectral analysis, varies during its 50 μs existence, rising sharply from an initial temperature of about 20,000 K to about 30,000 K, then dropping away gradually to about 10,000 K. The average is about 20,400 K (20,100 °C; 36,300 °F).^[2] This heating causes it to expand outward, plowing into the surrounding cooler air at a speed faster than sound would travel in that cooler air. The outward-moving pulse that results is a shock wave,^[3] similar in principle to the shock wave formed by an explosion, or at the front of a supersonic aircraft. More recently, the consensus around the cause of the shock wave has been eroded by the observation that measured overpressures in simulated lightning are greater than could be achieved by the amount of heating found. Alternative proposals rely on electrodynamic effects of the massive current acting on the plasma in the bolt of lightning.^[4] This shockwave is sufficient to cause injury, such as internal contusion, to individuals nearby.^[5] Inversion thunder results when lightning strikes between cloud and ground occur during a temperature inversion. In such an inversion, the air near the ground is cooler than the higher air. The sound energy is prevented from dispersing vertically as it would in a non inversion and is thus concentrated in the near ground layer. Inversions often occur when warm moist air passes above a cold front; the resulting thunder sound is significantly louder than it would be if heard at the same distance in a non inversion condition.^[6]

Thunder is the sound produced by lightning.

Etymology

The d in Modern English thunder (from earlier Old English þunor) is epenthetic, and is now found as well in Modern Dutch donder (cp Middle Dutch donre, and Old Norse þorr, Old Frisian þuner, Old High German donar descended from Proto-Germanic *þunraz). In Latin the term was tonare "to thunder". The name of the Germanic god Thor comes from the Old Norse word for thunder.^[7]

The shared Proto-Indo-European root is *tón-r̥ or *tar-, also found Gaulish Taranis and Hittite Tarhunt.

Calculating distance

A flash of lightning, followed after some seconds by a rumble of thunder is, for many people, the first illustration of the fact that sound travels significantly slower than light.^{[citation needed]} Using this difference, one can estimate how far away the bolt of lightning is by timing the interval between seeing the flash and hearing thunder. The speed of sound in dry air is approximately 343 m/s or 1,127 feet per second or 768 mph (1,236 km/h) at 20°C (68 °F).^[8] However, this figure can only be used as an approximation of the speed of a thunder-clap, as you are unlikely to find dry air in a thunderstorm.

The speed of light is high enough that it can be taken as infinite in this calculation because of the relatively small distance involved. Therefore, the lightning is approximately one kilometer distant for every 2.9 seconds that elapse between the visible flash and the first sound of thunder (or one mile for every 4.6 seconds). In the same five seconds, the light could have travelled the same distance as circling the globe 37 times. Thunder is seldom heard at distances over 20 kilometers (12 mi).^[3] A very bright flash of lightning and an almost simultaneous sharp "crack" of thunder, a thundercrack, therefore indicates that the lightning strike was very near.

See also

• Thunderstorm
• Thunderbolt
• Lightning
• Brontophobia (fear of thunder)
• Mistpouffers
• The Castle Thunder sound effect
• List of thunder gods
• Thursday (day of Thor)

References

1. ^ Rakov, Vladimir A.; Uman, Martin A. (2007). Lightning: Physics and Effects. Cambridge, England: Cambridge University Press. p. 378. ISBN 0-521-03541-4. 
2. ^ Cooray, Vernon (2003). The lightning flash. London: Institution of Electrical Engineers. pp. 163–164. ISBN 0-85296-780-2. 
3. ^ ^{a b} "Thunder". Encyclopædia Britannica. http://www.britannica.com/EBchecked/topic/594339/thunder. Retrieved 2008-09-12. 
4. ^ P Graneau, The cause of thunder, 1989 J. Phys. D: Appl. Phys. 22 1083-1094 doi:10.1088/0022-3727/22/8/012
5. ^ Fish, Raymond M (2004). "Thermal and mechanical shock wave injury". In Nabours, Robert E. Electrical injuries: engineering, medical, and legal aspects. Tucson, AZ: Lawyers & Judges Publishing. p. 220. ISBN 1-930056-71-0. 
6. ^ http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA477220
7. ^ "thunder". Oxford English Dictionary (2 ed.). Oxford, England: Oxford University Press. 1989. 
8. ^ See, for example, page 14-36 of Handbook of Chemistry and Physics, 72nd edition, special student edition. Boca Raton: The Chemical Rubber Co.. 1991. ISBN [[Special:BookSources/08493056259|08493056259]]. 

External links

• The science of thunder

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - torden, bulder
v. intr. - tordne, buldre
v. tr. - sige noget med tordnende stemme

Nederlands (Dutch)
donder, gedonder, donderen, denderen, bulderen met iemands idee(ën) goede sier maken

Français (French)
n. - (Météo) tonnerre, fracas, grondement, tonnerre (de)
v. intr. - tonner, faire un bruit de tonnerre (sur), tempêter, passer dans un bruit de tonnerre
v. tr. - hurler, tonner, faire éclater (un tonnerre d'applaudissements)

Deutsch (German)
n. - Donner, Donnern, Donnerwetter
v. - donnern, tosen, brüllen, ein Donnerwetter loslassen

Ελληνική (Greek)
n. - βροντή, μπουμπουνητό, κεραυνός
v. - βροντώ, μπουμπουνίζω, βροντοφωνάζω, μιλώ ή εκφράζομαι έντονα

Italiano (Italian)
tuonare, tuono

idioms:

• steal a person's thunder    rubare le idee di

Português (Portuguese)
n. - raio (m), trovão (m), trovoada (f), censuras (f pl), estrondo (m)
v. - trovejar

idioms:

• steal a person's thunder    roubar a idéia de outro

Русский (Russian)
грохотать, греметь, гром

idioms:

• steal a person's thunder    перехватить инициативу, добиться преимущества, перехватить приоритет

Español (Spanish)
n. - trueno, estruendo
v. intr. - tronar, retumbar
v. tr. - proferir como un trueno, lanzar, fulminar, golpear repetidamente, expresar con aplausos

Svenska (Swedish)
n. - åska, dunder, dån
v. - åska, dundra, dåna, braka

中文（简体）(Chinese (Simplified))
雷, 轰隆声, 雷声, 打雷, 怒喝, 轰隆地响, 轰隆地发出, 厉声发出吼出, 砰然重击

中文（繁體）(Chinese (Traditional))
n. - 雷, 轟隆聲, 雷聲
v. intr. - 打雷, 怒喝, 轟隆地響
v. tr. - 轟隆地發出, 厲聲發出吼出, 砰然重擊

한국어 (Korean)
n. - 우뢰, 고함, 비난
v. intr. - 천둥 치다, 큰 소리를 내다, 탄핵하다
v. tr. - 고함지르다, 발사하다, 큰 소리로 말하다

日本語 (Japanese)
n. - 雷, 雷のような音, とどろき
v. - 雷が鳴る, とどろく, 大声で言う, 激しく非難する

العربيه (Arabic)
‏(الاسم) رعد (فعل) ترعد السماء‏

עברית (Hebrew)
n. - ‮רעם, רעש, זעם‬
v. intr. - ‮רעם, הרעים בקולו‬
v. tr. - ‮רעם, איים, ביקר בחריפות‬

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